Shutdown controllers and load controllers generally, are applied in wind turbines for protecting the tower, blades, transmission, generator and other components against structural overload.
The load on a wind turbine structure mainly derives from wind pressure on the rotor plane and tower. Accordingly, the load depends on the wind speed, turbulence, wind density, and various settings including blade pitch angle and yaw angle. The latter expresses the angle of the rotor shaft relative to the direction of the wind.
The loads are traditionally measured by various sensors which measure various mechanical states of the turbine, herein referred to as mechanical-state-sensors.
Examples of such sensors include sensors for sensing rotational speed, oscillation level e.g. measured as tower acceleration, blade load e.g. measured by strain gauges fixed in the blade root, and blade pitch angle sensors determining the angle of attack of the wind and thus the degree of wind energy to rotor energy conversion which can take place.
Conventional turbine shutdown is based on unitary sensor inputs where one sensor signal measures a state, e.g. rotor speed, and a shutdown is initiated when the signal reaches a predetermined limit.